Final answer:
Most inherited forms of cancer, like mutations in the BRCA1 gene, show a dominant pattern of inheritance in a pedigree. However, the formation of cancer is actually recessive at the cellular level. This is because it requires multiple mutations in different genes, not just a single mutation.
Step-by-step explanation:
In most inherited forms of cancer, like the mutation in the BRCA1 gene, there is a dominant pattern of inheritance in a pedigree. This means that individuals who inherit the mutated gene are at increased risk of developing cancer. However, at the cellular level, the formation of cancer is actually recessive. This is because cancer development requires multiple mutations in different genes, not just a single mutation in BRCA1.
For example, the BRCA1 gene is a tumor suppressor gene. It helps regulate cell growth and prevent the development of tumors. When a mutation occurs in BRCA1, the gene loses its ability to suppress tumor growth. However, a single mutated copy of BRCA1 is usually not enough to cause cancer. The other copy of the gene, which is normal, can still provide some tumor-suppressing function.
In order for cancer to develop, both copies of BRCA1 need to be mutated. This typically requires a second mutation to occur in the normal copy of the gene. Once both copies of BRCA1 are mutated, the tumor-suppressing function is completely lost, allowing for uncontrolled cell growth and the development of cancer.
Therefore, while the inherited mutation in BRCA1 increases the risk of developing cancer, it does not guarantee that an individual will develop the disease. It requires additional mutations in the other copy of BRCA1, as well as potentially other genes, for cancer to form. This is why the formation of cancer is considered recessive at the cellular level, even though the inheritance pattern in a pedigree is dominant.